Wrapping things up, there’s little we need to say that wasn’t already evident in our graphs. The 6990 is a halo card and succeeds at such – by packing two Cayman GPUs on a single card, it is without question the fastest video card on the market today. At the same time there is and always will be a distinction between single-GPU cards and dual-GPU cards; the former is a threat to the latter, but the latter is rarely a threat to the former.

When we reviewed the Radeon HD 5970 back in 2009, the principle question we ran in to was whether it would be better to have a 5970 or two 5850s in CrossFire, given that the two were nearly identical in performance. The answer was that CrossFire was superior so long as you had a power supply with four readily available PCIe power plugs. With the Radeon HD 6990, we find ourselves asking the same question and an even more direct answer. With but a trio of exceptions, the 6990 doesn’t make sense compared to a pair of cards in CrossFire.

The reasons for this are numerous. The 6990 is so close to the 6950CF in performance that on average at 2560 the two are identical. It’s only in Bad Company 2 and Stalker that we see the 6990 take an advantage, which is then negated by anything from Civilization V to DIRT 2. Meanwhile the 6950CF is cooler, significantly quieter, and less power hungry than the 6990. And finally the 6950CF is cheaper: we can snag a pair of cards for $520, versus $700 for the 6990. Likewise, for $640 you can have a pair of 6970s and enjoy performance at 2560 roughly 8% ahead of the 6990, and that setup is still quieter than the 6990.

This leads us to our exceptions, and why we believe the 6990 is truly a niche product.

Quad-CrossFire; this is going to be the highest performing AMD solution at this time, power and noise be damned. This requires a motherboard with PEG slots three slots apart (lest you choke the first 6990), but it’s achievable.

5x1P Eyefinity. At five-panel resolutions you’re going need a pair of powerful GPUs, but given AMD’s CrossFire Eyefinity limitations at the time only 2 cards can directly drive five monitors: the 5870 Eyefinity 6, and the 6990. Ultimately MST hubs will allow the 6970CF to do this, but for the time being the 6970CF is limited by the number of displays a single card can drive without a hub.

If you absolutely cannot fit two cards in your computer. This is often the traditional domain of the dual-GPU card, but the 6990’s cooling and power requirements put this in jeopardy. Most micro-ATX cases would simply not be suitable due to cooling needs, meanwhile motherboards with two or more PEG slots are increasingly common. There are very few computers with a single PEG slot that could power and cool the 6990 without a complete overhaul in the first place.

Dual-GPU cards have always been a niche product, but the 6990 really takes this and runs with it. There’s no significant power/noise savings to be found by consolidating two GPUs on to a single card, and as we said earlier with the dual-exhaust cooler the 6990 is effectively two video cards on one PCB. This isn’t a bad thing – the 6990 is the world’s fastest video card after all – but it drives the card in to some very specific niches. If you fall in to these niches, then the 6990 is certainly the card for you. At 22% faster than the 5970 it isn’t a massive performance boost, but it certainly has earned its place.

But if you don't fall into these niches, then there’s nothing the Radeon HD 6990 offers you today that the 6950/6970 didn’t offer in CrossFire mode yesterday. In this case while AMD’s king card is an engineering marvel for its ability to handle so much power in a confined space, as a product on the market it won’t be quite as significant as the title implies.

I'm disappointed at the choices AMD made with the cooler. The noise levels are truly intolerable, it seems like it would have made more sense to go with a triple-slot card that would be more capable of handling the heat without painful levels of noise. It'll be interesting to see how the aftermarket cooler vendors like Arctic Cooling and Thermalright handle this.Reply

There's actually a good reason for that. I don't believe I mentioned this in the article, but AMD is STRONGLY suggesting not to put a card next to the 6990. It moves so much air that another card blocking its airflow would run the significant risk of killing it.

What does this have to do with triple-slot coolers? By leaving a space open, it's already taking up 3 spaces. If the cooler itself takes up 3 spaces, those 3 spaces + 1 open space is now 4 spaces. You'd be hard pressed to find a suitable ATX board and case that could house a pair of these cards in Crossfire if you needed 8 open spaces. Triple slot coolers are effectively the kryptonite for SLI/CF, which is why NVIDIA isn't in favor of them either (but that's a story for another time).Reply

if it means a quieter card then that might have been a compromise worth making. Also, 2.5 would stop people from making the il-advised choice of using the slot next to the card, thus possibly killing it!Reply

However, if one is even contemplating Crossfire or SLI then a triple-slot space between the PCIe X16 SOCKETS for a pair of high-power 2-slot-cooler graphics cards with "open-fan" cooling (like the 6990) is recommended to avoid one card being fried by lack of air. This socket-spacing allows a one-slot clear air-space for the "rear" card's intake fan to "breathe". (Obviously, one must not plug any other card into any motherboard socket present in this slot)

In the case of a pair of 6990 (or a pair of nVidia's upcoming dual-GPU card), a minimum one-slot air-space between cards becomes MANDATORY, unless custom water or cryo cooling is installed.

Very few current Crossfire/SLI-compatible motherboards have triple-slot (or more) spaces between the two PCIe X16 connectors while simultaneously also having genuine X16 data-paths to both connectors. That socket spacing is becoming more common with high-end Sandy-Bridge motherboards, but functionality may still may be constrained by X8 PCIe data-paths at the primary pair of X16 connectors.

To even attempt to satisfy the data demands of a pair of 6990 Cross-Fire with a SINGLE physical CPU, you really do need a X58 motherboard and a Gulftown Corei7 990x processor, or maybe a Corei7 970 heavily overclocked. For X58 motherboards with triple-spaced PCIe sockets properly suitable for Crossfire or SLI , you need to look at the Asrock X58 "Extreme" series of motherboards. These do indeed allow full X16 data-paths to the two primary PCIe X16 "triple-spaced" sockets.

Many ATX motherboards have a third "so-called" PCIe X16 socket in the "slot7" position. However, this slot is always incapable of a genuine X16 pairing with either of the other two "X16" sockets, Anyway this "slot 7" location will not allow any more than a two-slot wide card when the motherboard is installed in a PC "tower" -- an open-fan graphics card will have no proper ventilation here, as it comes right up against either the power-supply (if bottom-loaded) or the bottom-plate of the case.Reply

Exactly. For people who are going to do quad-Crossfire with these, you pretty much have to add the cost of a liquid cooling system to the price of the cards, and it's going to have to be a pretty studly liquid cooler too. Of course, the kind of person who "needs" (funny, using that word!) two of these is also probably the kind of person who would do the work to implement a liquid cooling system, so that may be less of an issue than it otherwise might be.

So, here's the question (more rhetorical than anything else). For a given ultra-high-end gaming goal, say, Crysis @ max settings, 60fps @ 3x 2500x1600 monitors (something that would require quad Crossfire 69xx or 3-way SLI 580), with a targeted max temperature and noise level... which is the cheaper solution by the time you take into account cooling, case, high-end motherboard, the cards themselves? That's the cost-comparison that needs to be made, not just the cost of the cards themselves.Reply

Before anyone thinks of buying this card stock, you should really go out and get a sense of what that kind of noise level is like. Unless you have a pair of high quality expensive noise-cancelling earbuds and you're playing games at a loud volume, you're going to constantly hear the fan.

$700 isn't the real price. Add on some aftermarket cooling and that's how much you're going to spend.